1. Field of the Invention
The present invention relates to a data transmission system for transmitting data over a LAN or the like and a method thereof.
2. Description of the Related Art
There is generally used a VLAN (Virtual LAN) which utilizes one LAN (Local Area Network) as if it were a plurality of LANs.
In the VLAN, unicast transmission for transmitting certain data to one destination and multicast/broadcast transmission for transmitting the same data to a plurality of destinations are performed.
For example, a network management system and switching HUB unit in the VLAN have been disclosed in Japanese unexamined patent publication H11-313073 and Japanese unexamined patent publication 2000-13429 (references 1 and 2).
The method to perform transmission control by giving an identifier (VLAN-ID) to each of VLANs and adding the VLAN-ID to a MAC (Media Access Control) frame (IEEE802.3) as a tag (defined in IEEE802.3Q) is also referred to as TAG-VLAN.
A switching device referred to as switching HUB or the like is used for data transmission in the VLAN.
This switching device generally performs processes in a MAC layer belonging to a second layer (data link layer) of an OSI reference model.
That is, when receiving the transmission frame (MAC frame) of the multicast/broadcast, the switching device generally outputs the received transmission frame to all ports regardless of whether a node belonging to the same VLAN as a node at the transmission source is connected, or a node belonging to a different VLAN is connected.
As described above, control of the transmission frame, which has been sent beyond the VLAN (segment), is left to process in an IP layer of a TCP/IP protocol group corresponding to the third layer (network layer) of the OSI reference model.
If the transmission frame of multicast/broadcast can be confined within each of the VLANs to be transmitted by a process in the MAC layer, it goes without saying that it will be possible to restrain network traffic, and to reduce the load of the communication node and that it will also be advantageous in terms of security and the like.